Java™ Application Development on Linux - Dator

392Chapter 17Other Ways: Alternatives to SwingCAUTIONIf a Composite has no layout manager, each Widget in the Compositemust have its size and position explicitly set, or else their sizes will default tozero, and they will all be invisible! Tremendous details on SWT layout managerclasses can be found in the article “Understanding Layouts in SWT” by CarolynMacLeod and Shantha Ramachandran on the Eclipse Web site. 1317.3.3.2 Converting the GUI init() MethodThe setStatus() method is called whenever the data in the core modelchanges. Its job is to update the UI to reflect those changes. More specifically,it updates the status pane at the top of the UI. There are correspondingmethods for the list pane and the button pane.Oddly, there are no changes in this particular method. The purpose of thismethod is unchanged. It updates the Labels with the new numbers and checksto see if the current Account is the top level Account. If it is, the Up buttonis disabled, otherwise it is enabled.It turns out that all of the methods called on the UI classes in this methodhave the same names and purposes in Swing and SWT. Don’t assume this willbe true in the other cases.17.3.3.3 Reworking Event HandlersFinally, in the litany of conversion, we have to modify the event handlers. Inthis case, the only event of interest is when the Up button is pressed. Pressinga Button produces a Selection event.In SWT, there are several types of events. Generally, you specify a classthat will handle the event by calling one of the add...Listener() methodson the Widget that you wish to process the event for. Examples of thesemethod calls include:• addSelectionListener()• addControlListener()• addFocusListener()• addHelpListener()13. http://www.eclipse.org/articles/Understanding%20Layouts/Understanding%20Layouts.htm